A direct combustion apparatus hitherto employed for removing malodorous substances discharged from a paint plant and other various plants is designed to heat an objective gas to about 800.degree. C., oxidize the malodorous substances, and decompose into odorless carbon dioxide and water. It is known as a deodorizing apparatus and has a wide scope of applications. In addition, it is capable of treating all malodorous substances that are oxidized and decomposed at a high temperature. A drawback of this direct combustion apparatus is its high fuel cost. In other words, the combustion heat of the malodorous substances is lowered as the concentration of the malodorous substances is lowered, which leads to increase of the fuel amount, thereby increasing the cost.
A prior art device which uses a reduced fuel amount and has an exceptional heat recovery rate is disclosed in FIG. 22. First, second, and third columns 1, 2, 3 filled with a heat reserve material such as ceramics are provided. Burners 4, 5 are disposed so that the temperature of the top of each column reaches about 800.degree. C. The objective gas containing malodorous substances is guided into a duct 6, which is linked to the lower part of each column 1, 2, 3 through valves 7, 8, 9. The gas purified through valves 10, 11, 12 is discharged through a duct 13.
During operation, the objective gas from the duct 6 is raised, for example, from the lower part of the second column 2 through the valve 8, and is heat-exchanged. The malodorous substances are oxidized and decomposed by the burner 5. A heat reserve material 14 in the third column 3 is heated to reserve heat. The purified gas is discharged from the duct 13 through the valve 12, and exhausted to the atmosphere. The valves are changed over by a timer, and purging air is supplied from a duct 15 into the lower part of the second column 2 to move the malodorous gas in the second column 2 into the first column 1. The objective gas to be processed next is guided into the lower part of the third column 3 through the valve 9 from the duct 6, and is heated by the heat reserve material 14. The malodorous substances are oxidized and decomposed by the burner 4. The heat reserve material in the first column 1 is heated to exchange heat, and the purified gas is moved into the duct 13. Afterwards, the purging air is further supplied into the lower part of the third column 3 from the duct 15, and is conducted into the second column 2 through the burner 5. The objective gas is supplied into the lower part of the first column 1 through the valve 7 from the duct 6, and heated by the heat reserve material. The malodorous substances are oxidized and decomposed by the burner 4, and the gas purified through the valve 11 from the second column 2 is discharged from the duct 13 together with the air for purge. In this way, sequentially in time by the timer, the objective gas rises through the first to third columns 1, 2, 3, and absorbs the heat from the heat from the heat reserve material 14. The gas heated by the burners 4, 5 descends through the first, second and third columns 1, 2, 3 to heat the heat reserve material 14, so that the heat recovery rate may be enhanced greatly.
A problem of the prior art shown in FIG. 22 is that it requires a total of three large-sized columns 1, 2, 3 for the purpose of purging. Before changing from the heat absorption process of the objective gas into the heat release process, the malodorous gas remaining in the columns 1, 2, 3 without being decomposed must be purged. Although the amount of air necessary for this purge is substantially smaller as compared with the flow rate of the objective gas, the prior art device shown in FIG. 22 requires the columns to have the same volume as the columns for heat absorption-release, and the facility cost is high, and a wider area for installation is needed. Moreover, it requires a total of six changeover valves 7, 8, 9, 10, 11, 12, and also three purging changeover valves. Therefore, the construction is complicated and expensive.
Moreover, in the prior art device shown in FIG. 22, the changeover operation of the valves 7, 8, 9, 10, 11, 12 is a so-called semi-batch operation, and the changeover operation is done, generally, every two minutes or so. The required amount of heat reserve material is determined by this changeover time. Thus, a changeover operation every one minute requires about half the two-minute amount, and the required amount of heat reserve material is about one-quarter the two-minute amount when changing over every 30 seconds. But the prior art device shown in FIG. 22 requires an operation time dependent upon the valves 7, 8, 9, 10, 11, 12, and the time required for purging a massive volume of air is long. Hence, it is difficult to shorten the changeover time of the valves 7, 8, 9, 10, 11, 12, and as mentioned above, the required amount of the heat reserve material increases.
FIG. 23 shows other prior art device which has an exceptional heat recovery efficiency and is capable of saving the fuel consumption for the purpose of downsizing the constitution. In this prior art device, the objective gas containing malodorous substances is supplied from a duct 17, and is moved into an upper space 20 of a housing 19 via a changeover valve 18. As it flows through the heat reserve material 21, it is heated by the heat reserve material 21, and is further heated by an electric heater 22 to about 1000.degree. C. The heat is released to a heat reserve material 23 beneath, and as a result heat is accumulated in the heat reserve material 23. The gas is then discharged through a changeover valve 18 and a duct 25 from a lower space 24. Then the changeover valve 18 is changed over, and the objective gas from the duct 17 passes through the space 24. The gas is next heated by the heat reserve material 23, and is further heated by the electric heater 22. The heat is then released to the heat reserve material 21 thereby accumulating heat. Finally, the gas is discharged from the duct 25 through the changeover valve 18 from the space 20. Such operation is then repeated.
In the prior art shown in FIG. 23, immediately after changeover operation of the changeover valve 18, purging is not carried out, and hence the objective gas containing malodorous substances is partly discharged through the duct 25. A different prior art device for solving this problem is disclosed in FIG. 24. In this prior art device, the corresponding parts similar to those of the prior art device shown in FIG. 23 are denoted with the same reference numerals. This prior art device has further changeover valves 27, 28, and also has a purge tank 30 communicating with the atmosphere.
In this prior art device, the objective gas containing malodorous substances is passed through the changeover valve 18 from the duct 17, and is heated by the heat reserve material 21 from the space 20 in the housing 19. The gas is further heated by the electric heater 22, and the heat is reserved in the heat reserve material 23. Then, a purified gas is discharged through the valve 27 from the changeover valve 18 and the duct 25. At this time, the changeover valve 28 is closed. Immediately after the changeover valve 18 is changed over, the changeover valve 27 is closed and the changeover valve 28 is opened. Gas is moved from the duct 17 through the changeover valve 18 and from the space 24 in the housing 19 through the space 20. In addition, gas is moved through the changeover valves 18, 28, and then stored in the tank 30. After storing a necessary amount for purge, the changeover valve 28 is closed, the changeover valve 27 is opened, and the exhaust gas is exhausted through the changeover valve 27. The air containing malodorous substances stored in the tank 30 immediately after the changeover is later passed gradually into the duct 17 through the duct 31, and is mixed into the objective gas.
This prior art device shown in FIG. 24 has problems that the large column tank 30 for purge is required, time for changeover operation of the changeover valves 18, 27, and 28 is necessary, and a large amount of heat reserve material is required. Such problems are the same as experienced in the prior art mentioned in FIG. 22.
A different prior art device is disclosed in U.S. Pat. No. 5,016,547. In this prior art, heat reserve materials are disposed in plural segments partitioned in a housing in the peripheral direction. A changeover valve having a valve disc disposed beneath the housing is rotated. The objective gas is then elevated and heated by the heat reserve materials, and flammable components of the objective gas are burnt in a combustion chamber above the housing. A purified gas containing no flammable component passes through the heat reserve materials and descends while heating the heat reserve materials. The purified gas is discharged outside through the changeover valve, and the changeover valve sequentially changes over each of such segments in the peripheral direction. Such fundamental constitution is similar to the principle of the present invention, except that in the prior art, a pair of purge gas passages are formed at positions deviated from each other by 180 degrees in the peripheral direction to prevent the objective gas remaining in the segment from entering into the purified gas. The prior art device thus prevents objective gas from being discharged at the time the segments of the heat reserve materials are changed over by the changeover valve so that the purified gas may descend.
A problem of this prior art is that a pair of purge gas passages are formed, thereby decreasing the heat reserve materials, i.e. the effective volume used to treat the objective gas and produce clean gas. Moreover, the structure of the changeover valve for forming the two purge gas passages is complicated. Furthermore, since gas is supplied into the pair of purging gas passages, the required flow rate of purge gas is increased.